1. Field of the Invention
The present invention relates to a self-drilling screw having a shaft provided with a thread at least in some of its regions and defining a longitudinal axis, a drilling tip provided at one end of the shaft, a head provided at another, opposite end of the shaft, and at least one first cutting edge and at least one second cutting edge both provided in the drilling tip.
2. Description of the Prior Art
U.S. Patent Publication US 2004/0018069 discloses a self-drilling screw having a shaft, a head provided at one end of the shaft, and a drilling tip provided at the end of the shaft remote from the head. The drilling tip has a first cutting edge located in the radially outer region of the drilling tip, and a second cutting edge extending from a radially inner region to the radially outer region. The first cutting edge extends to the longitudinal axis of the self-drilling screw at a first acute angle, and the second cutting edge extends to the longitudinal axis at a second acute angle that is smaller than the first acute angle.
The drawback of such self-drilling screw consists in that the bore diameter can vary, dependent on an applied press-on force during the setting process of the self-drilling screw because at a small press-on force, the drilling tip can tumble. Therefore, at a small applied press-on force, a larger bore is formed, which leads to a smaller holding value.
Accordingly, an object of the present invention is to provide a self-drilling screw in which the drawback of the known self-drilling screw is eliminated, and a predetermined borehole diameter is provided over the entire borehole length.
Another object of the present invention is to provide a self-drilling screw that insures a more rapid drilling feed at a smaller press-on force.